Here is a list of all the postings blowlamp has made in our forums. Click on a thread name to jump to the thread.
|Thread: The boat that Guy built|
|For those that remember them, some of the BBC's Horizon and Channel 4's Equinox documentaries made for excellent viewing.|
There also seems to be a belief with many of the programme makers that if we're not singing, dancing, or laughing, then we can't be having fun or enjoying ourselves.
I've also noticed the 'fear' of the producers of anyone having a meaty chat about things mechanical as it's always done in a jokey way, as if it's too painful for the viewer otherwise.
It is interesting to see how they're trying to remind the population of our manufacturing past and I wonder if those in charge are hinting at what we should be doing now, with programmes like this, along with the very interesting documentory Britain At Work, which is presented quite nicely by Kirsty Young. After all, now it's so expensive to buy a degree, many school leavers may need to go back into manufacturing whatever we can.
|Thread: Mystery Tools|
It's hard to tell for sure, but the last pic looks like it could be a Spade Drill.
|Thread: Trouble posting to forum!|
I'm using Windows 7 along with Internet Explorer 9 (release candidate) and am really quite pleased with the combination.
I'm not a 'fan boy' of Microsoft, but I appreciate the free lifetime support and updates of their operating systems, as well as their other totally free stuff, such as Security Essentials, which is a virus/spyware protection application and I'm finding it to be as effective as anything else available, without slowing the system.
I started a thread about what I consider to be the deficiencies of this site with regard to things like attachments of files and pictures etc.
Edited By blowlamp on 23/02/2011 00:14:18
|Thread: Moving photos between albums|
I can't help with your query, but just in case you didn't know, you should take care if you have previous forum posts with pictures that reference back to your album(s) here. Moving pictures from an album will cause that picture to be erased from your post too.
|Thread: Help Please|
+1 for Super Glue. It's great for split finger nails when the fracture goes down to that bit that really hurts and you keep catching it on clothes and stuff.
Edited By blowlamp on 30/01/2011 15:10:21
Edited By blowlamp on 30/01/2011 15:10:51
|Thread: Time for new forum software.|
My point is that the lack of facilities here, coupled with the faults in formatting are largely not issues at other webites that I visit. Also, I believe IE9 will become the next standard - whether we like it or not - in the same way the other IEx's have been in the past.
I'm using the beta version of Internet Explorer 9 so some of my issues could be related to that, but put bluntly, the forum software here is just about as bad as it gets.
There's no way to include pictures in a post without creating an album and linking to it. If you then remove that picture from the album, the picture disappears from your forum post, which just looks sad .
There are no attachment facilities either, so you can't help people with things like their software or drawing problems.
Formatting always messes up for me after posting with Line Feeds and Spaces being randomly removed etc.
Advertisements quite often cover postings making them unreadable.
You can't see who else is online.
It's just way behind the rest, where all the above comes as standard.
|Thread: Watch manufaturing|
You could have a go at making your own like this fella does.
|Thread: C A D for Mac|
Downloads of ViaCAD, suitable for both Mac and PC, can now be had from here http://www.punchcadlabs.com/
|Thread: Parting off on Myford lathes|
To answer your last posts.
"If you didn't intend to compare the two why use the comparison?"
I didn't compare drilling with parting-off. I simply used drilling as an easily verifiable example of the effect of chip crowding i.e., the drill bit stops turning when jammed with swarf.
"It seems disingenuous to me."
Read the post again and you should see that it isn't.
"I'm sorry but so called 'chip crowding' takes place over a relatively long period of the process (several seconds) "
"I'm surprised that you are not aware of this so called phenomenon happening."
I am, I was the one that mentioned it first.
"By the way, if chips are jamming so firmly, how come they can simply 'fall out' when a rear toolpost is used, by the simple effect of gravity?"
The majority of them fall out of the way because there is no parting-off blade underneath them to block their exit.
When compared to a front mounted parting-off tool setup, it's obvious that swarf will rest upon the upper surface of the blade by the effect of gravity and by that same effect, along with vibration, the smaller particles can tend to collect in any gaps that are present, thus magnifying the chances of a log-jam style cram-up.
"As to your last point - with all due respects, 15 to 20mm depth of HSS parting tool, which is the normal size as most engineers are aware, I assumed that someone as perceptive as yourself would understand that without it having to be explained."
Well you wrote 15 to 20 mm wide and knowing what a stickler you are in your writing, I took you at your word. You made a straightforward mistake, but instead of correcting it, you're trying to put me on the spot for asking if what you wrote, was what you really mean to say - now that's disingenuous.
Edited By blowlamp on 22/01/2011 00:58:54
Just to clarify the position. My last post was only intended to reinforce my point about the effect chip crowding can have with regard to it's catastrophic consequences, rather than be a direct comparision with parting-off in the lathe.
I don't quite follow yourpoint about seeing and removing chip crowding from the groove, because my experience (in the dim and distant past of course) is it's pretty well over by then
WOW!! Is that a 15-20mm wide parting-off tool you mention towards the end
If anyone needs further evidence of the effect that chip crowding has, you only have to drill deep holes in certain materials such as aluminium to see how easily it can jam the bit.
Another example is if you try to deepen an already threaded hole at core size. In this instance the swarf is forced back down the hole as it rotates with the bit and is grabbed by the thread section of the hole.
Both are easy to verify for oneself.
Edited By blowlamp on 21/01/2011 14:00:54
Right, second bite...
So what we've established so far is that chatter is always present, but with care in the design of the machine, tooling and by using appropriate speeds etc, we can tune it out of harms way and so produce good work.
This is my take on what happens and is what I believe causes parting-off problems with the commonly available HSS blades when used in the front toolpost:
1/ The cut commences and is initially fine.
My View Is That:-
Depite the tool being quite wide and so removing more material than in normal turning, the basic Machine/Tool/Speed setup is adequate for the job.
2/ Once a certain depth is reached, sensations can be felt through the lathe and the sound of the cut can change. At this point I would say a lot of people instinctively withdraw the tool, clean the groove and carry on.
My View Is That:-
This is the point that the system is beginning to become unstable.
3/ A short while after the cut is recommenced, the cram-up happens - but why?
My View Is That:-
The parting-off blade is now working in a confined space with very, very little clearance.
As various sized chips are generatedby the cutting action, most of the larger ones are ejected by other swarf as it is being produced. However, small, gritty size pieces can remain and some of these will become lodged between the tool and the workpiece and might even 'pick-up' or 'gaul' the job.
From there, it can be seen that this unstable system is working in a situation where a log-jam can now occur as other swarf is produced.
When the log-jam does happen, the system experiences large forces and from these forces deflections can be seen about the tool and it's mounting, as well as the visible signs of the work moving too.
So to work around the problem:-
Some folks will widen the groove, before carrying on with the first cut as it gives more room for the swarf to clear.
Some will part-off from the rear, which allows gravity to help keep the groove clear of swarf.
Others will use a specially designed 'tipped' tool which curls the chip to make it narrower and also has plenty of clearance at the sides.
Edited By blowlamp on 21/01/2011 12:30:41
Edited By blowlamp on 21/01/2011 12:31:35
|Thread: C A D for Mac|
ViaCAD is the software I've chosen for use on my PC and is also available for the Mac.
Note that demo downloads aren't available on the website at the moment, since it was revamped and apparently were left out by mistake. They should be back on again soon, but if anyone is desparate I can forward an email address to you by PM, where you can ask to be sent a link.
|Thread: Parting off on Myford lathes|
Thanks for this very interesting reply, but in it, you seem to be concentrating on chatter, rather than the topic of parting-off.
When I've had parting-off cram-ups in the past, I don't particularly remember chatter being part of the problem. It was more a sense of the lathe having a 'rough' feeling coming through the feed handle, accompanied by an unpleasant sound before the inevitable crack of the tool breaking.
Another comment I might make, is that if springiness in the drive system is the problem with these lathes, then I can't see how using a rear mounted toolpost can cure it, as we will still be using that same drive system along with all it's supposed inadequacies.
Did you find that using backgear eliminates the problem?
Edited By blowlamp on 19/01/2011 20:52:17
"I was not talking about wear or about belts slackening in use due to permanent deformation. I was talking about elasticity."
As I tried to point out, you are talking about the elasticity (acting as a spring) of the belt at a minute level, which in comparison to belt slip in this context, is inconsequential. You also stated that belts stretch, which I took you to mean as a permanent deformation.
"Like it or not, when you drive a spindle via a drive train, there is a measurable amount of elasticity in the drive train which, when coupled to the various spinning masses involved (motor armature, spindle, chuck, workpiece, plus any intervening shafts/pulleys/gears) forms a mechanical system that can be made to oscillate at one or more resonant frequencies..."
It's not a matter of if I like it - it's just fact.
If you take a look at my previous posts on this, you'll see I asked for clarification on this very point, by posing the question about how a geared-head lathe with a motor belt drive in the system, differs from the original poster's example (Myford).
As almost all lathes have a belt drive somewhere in the train and therefore have an 'elastic' transmission setup, it's strange that apparently these aren't susceptible in the same way as a Myford.
Edited By blowlamp on 19/01/2011 15:11:30
"Firstly, ALL belts, Myford or otherwise, stretch. Some stretch more than others, but they do stretch. And yes, that is what I mean when I say that they are elastic - if you want it in mechanical terms, they have a Young's modulus that is finite. So, if you apply a tension to the belt, it will stretch. Maybe not by much, but it WILL stretch. End of.
Secondly, given the above, and given that the gear train itself is also elastic (although not so much as the belt), yes, it does all apply to a greared train with or without a belt for primary drive. As I said earlier, the principle is the same; the variable is the degree of elasticity - a gear train is (generally) less elastic than a belt drive.
I was trying to keep the discussion reasonable, by speaking in practical terms of this particular topic, but if we are now at the microscopic level, yes drive belts are elastic. They are elastic in the same sort of way that a lump of granite or wood is, but not in the same way that a rubber band is.
If we're talking about belts slackening whilst in use, it will be seen as stretch by some, but I think it is more likely to be down to wear on the vee surfaces, which will allow the belt to sink deeper into the pulleys.
Any manufacturer worth his salt will choose materials that are appropriate for the job and a belt that progressively stretches, wont hold it's tension and will start to slip.
Edited By blowlamp on 19/01/2011 13:35:50
Edited By blowlamp on 19/01/2011 13:37:02
Myford drive belts are flexible, but they aren't stretchy - if that is what people are meaning when they say they are elastic.
I would still like an explanation as to why this theory doesn't apply to lathes that have geared heads and primary drive belts from the motor.
Taking a second cut creates a wider slot and simply gives more room for chip clearance.
Edited By blowlamp on 19/01/2011 11:02:34
Those drawings are put together in such a way as to reinforce the argument of the author.
To my way of thinking - and this is assuming that both the tool and toolpost are up to the job - then the pivot point should actually be at the front foot of the toolpost on the left, which is almost directly under the tip of the cutting tool.
In that position though, there is so little extension of the tool beyond it's support footprint, that there is practically no opportunity for a rocking movement to happen due to a downward force on the tool.
Non of the above helps the assertion of the rear toolpost being stiffer, as the strength of the tee-slot mounts must also called be called into question when evaluating it's merits.
Anyone with a Gibralter type toolpost should be able to verify that deflection is minimal when parting-off and thus do so with few problems, provided the groove can be reliably cleared of swarf. If a jam-up still occurs with a Gibralter - but not with the same tool mounted at the rear - then I'm pretty sure it's chip crowding.
All the above assumes a lathe in good condition.
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